1. Field of the Invention
The present invention is related to a fiber structure impregnated with low glass transition temperature viscous polymer adhesives and to articles made therefrom.
2. Description of the Related Art
Although many flexible body armor constructions adequately stop ballistic projectiles, the shock associated with blunt trauma can still cause substantial injury or death in an article such as a protective vest. Reducing the high level of blunt trauma can be accomplished by dissipating and spreading out the energy of impact.
Previously, stiffer layers have been provided near the body to reduce blunt trauma, but this is known to significantly compromise ballistic resistance to penetration and to add to the weight of the body armor, while reducing comfort.
International application (WO 2004/074761 A1) discloses visco-elastic polymer fluids that were solvent impregnated into ballistic fabrics and other related fiber containing ballistic sheets. Preferred range of glass transition temperature (Tg) is −128° C. to −40° C. Low viscosities of 0.25 Pa s to 2.5×104 Pa s were considered.
Briscoe, B. J., Motamedi, F., “Role of interfacial friction and lubrication in yarn and fabric mechanics”, Textile Research Journal 1990 6(12), 697 and Briscoe, B. J., Motamedi, F. “The ballistic impact characteristics of aramid fabrics: the influence of interface friction”, Wear 1992 158(1-2), 229 both describe medium viscosity polymer fluids that were impregnated into fabrics. Additives had a low Tg of −115° C. They found a lubrication effect as expected.
U.S. Pat. No. 6,701,529 to Rhoades et al disclose an energy absorbent medium of polymer, lubricant, and/or filler components that stiffens in proportion to the rate of an applied force. Polyborosiloxane polymer fluids and other hydrogen bonding polymer fluid mixtures exhibit dilatant (shear thickening) characteristics.
U.S. Pat. No. 3,649,426 and Lee, Y. S. et al. (N.J. Advanced Body Armor Utilizing Shear Thickening Fluids, 23rd Army Science Conference, 2002) consider shear-thickening suspensions of particles in conjunction with ballistic fibers.
WO 00/46303 and U.S. Pat. No. 3,649,426 describe polyaramid fabrics with shear-thickening particle suspensions in pouches or in back of polyaramid panels.
U.S. Pat. No. 5,776,839 discloses the application of dilatant dry powders, with a typical composition consisting of carbon black, fumed silica (nano-silica) and a small amount of adhesive “glue” to ballistic fibers and fabrics.
U.S. Pat. No. 5,229,199 considered rigid composites of woven aramid fabrics coated with an adhesion modifier and imbedded in a matrix resin. The reduced friction and weakened interfaces led to improved ballistic performance. If friction is too high in a fabric, or if the matrix is too stiff, ballistic resistance is severely compromised.
U.S. Pat. No. 5,354,605 used low Tg, high molecular weight elastomers as adhesive matrix materials for fiber layers. These provided flexibility in unidirectional ballistic layers.
U.S. Pat. No. 5,854,143 describes material for antiballistic protective clothing comprising, in a single-layer or multi-layer package or laminate, at least one layer of a flat structure containing a coated dry powder which is an organic dilatancy agent.
It is a desirable goal to improve resistance to blunt trauma in flexible body armor, while retaining the high ballistic resistance. Moreover, increased comfort and lower weight of ballistic vests are desirable properties to be achieved.